Acoustic energy is used in numerous applications to characterize discontinuities within various types of material. Acoustically based techniques rely on differences in mechanical properties between a feature of interest and its surroundings. These differences result in different vibrational responses to sonic excitation, which may be detected and the feature thereby localized and/or characterized.
An important advantage of acoustic techniques is the ability to detect discontinuities corresponding to (or indicating the presence of) flaws or hidden items that may not be detectable using visual or other techniques. Such discontinuities may represent latent defects that can compromise the mechanical integrity of load-bearing structures, dangerous concealed objects, or even buried landmines. A related advantage of acoustic detection is the standoff distance it affords. The ability to avoid physical contact may be desirable for reasons of convenience or safety.